title: Incidence and variants of posterior arch defects of the atlas vertebra.
abstract: In order to describe the incidence and existing variants of congenital anomalies of the atlas vertebrae in a Caucasian population, we examined 1069 CT scans of the upper cervical spine. We found 41 cases with altered atlas vertebrae, representing 3.8% of all analyzed patients. With 83% of all found anomalies, the predominant type is characterized by a small dorsal cleft (3.2% of all patients). Rare varieties feature unilateral or bilateral dorsal arch defects, combined anterior and posterior clefts (0.2% of all patients) or total erratic atlas vertebra malformation (0.1% of all patients). Atlas arch defects are found nearly 4% at the time. Most anomalies affect the posterior arch, whereas the anterior arch or both are rarely affected. Totally irregular C1 vertebrae are extremely infrequent.
authors.affiliation: University Hospital Zurich, Division of Trauma Surgery, 8091 Zurich, Switzerland.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Guenkel
authors.forename: Sladjana
authors.initials: S
authors.lastname: Schlaepfer
authors.forename: Sonja
authors.initials: S
authors.lastname: Gordic
authors.forename: Guido A
authors.initials: GA
authors.lastname: Wanner
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Simmen
authors.forename: Clément M L
authors.initials: CM
authors.lastname: Werner